1. Field of Invention
The present general inventive concept relates to devices that are useful in the manufacture of vehicle tires. More particularly, the present general inventive concept relates to an improved belt and tread drum having segments defining varied curvature.
2. Description of the Related Art
The manufacture of a vehicle tire commonly includes the steps of forming a tire carcass, forming a toroid-shaped belt and tread “package” of the tire separately from the carcass, and thereafter marrying the belt and tread package to the tire carcass to form a “green” tire. The green tire is thereafter treated to form the tread and various other features of a finished tire. Other supplementary steps, such as bonding the belt and tread package to the tire carcass (often referred to as “stitching” the belt and tread package), may be performed during the course of, or following, one or more of the aforementioned steps.
The formation of a tire carcass is typically performed using a tire building drum, of the type described in U.S. Pat. No. 6,457,505. Such a tire building drum typically defines a radially expandable and contractible cylindrical working surface upon which a tire carcass is formed. Subsequent to the formation of the tire carcass on the cylindrical working surface, such tire carcass may be transferred to an expansion drum, of the type discussed in U.S. Pat. No. 6,602,372. The tire carcass is positioned surrounding the expansion drum, and a portion of the tire carcass is overlaid with the belt and tread package. The tire carcass is then inflated to a toroid shape resembling, though often not identical to, the shape of a finished tire. While the tire carcass is inflated, the belt and tread package is joined to the tire carcass.
Formation of a belt and tread package of a tire is typically accomplished using a belt and tread drum, of the type disclosed in U.S. Pat. No. 6,013,147. Such a belt and tread drum typically has an outer cylindrical surface, or circumference, comprising a plurality of elongated segments, about which one or more layers of the tire belt material (comprising, for example, reinforcement cords embedded in a polymeric binder) are laid to define the belt and tread package. The circumference of the belt and tread drum is preferably capable of expanding and contracting to allow, for example, removal of a completed belt and tread package from the drum. A completed belt and tread package is typically essentially nonexpandable radially. However, a completed belt and tread package is typically flexible to the extent that, when unsupported, the toroid-shaped belt and tread package will deform and sag under the influence of gravity. Also, desirably, the adjustable circumference of the belt and tread drum enables a single drum to be used to form belt and tread packages of alternative diameters.
During formation of the belt and tread package on the belt and tread drum, it is not uncommon for the belt and tread drum and accompanying tooling to be configured such that the elongated segments of the belt and tread drum apply considerable pressure to interior surfaces of the belt and tread package, in part to assist in maintaining a uniform toroid shape of the tire component during formation. Such high pressures applied to the interior surfaces of the tire component can result in at least a portion of the arced exterior surfaces of the elongated segments becoming at least partially imprinted in the tire component, resulting in the formation of very slight imprints of the arcuate exterior surfaces of the elongated segments, and corresponding very slight bulges adjacent the imprints, in the tire component. Further, it is known that the radius of curvature of the various arcuate segments forming the belt and tread drum's outer cylindrical surface is fixed by the rigidity of the segments, thus rendering it impossible for the segments to be moved between radially expanded and contracted positions and collectively provide perfectly-formed cylindrical surfaces at each of these two positions. If, for example, the circumference of the drum is adjusted to a size at which the segments are positioned at a distance from the longitudinal axis which exceeds the radius of curvature of each segment arc, there will exist regions about the drum circumference where the circumferentially outward edges of the segments curve slightly radially inwardly from the central portions of the segments. Conversely, if the circumference of the drum is adjusted to a size at which the segments are positioned at a distance from the longitudinal axis less than the radius of curvature of each segment arc, there will exist regions about the drum circumference where the circumferentially outward edges of the segments project slightly radially outwardly from the central portions of the segments. In either case, the outer circumference of the belt and tread drum will be very slightly out of round. If these out of round regions are large enough (as may occur, for example, when the drum is expanded to allow manufacture of a tire of relatively large diameter), it is possible that the drum may produce undesirable alternating imprints and bulges of the slightly out-of-round exterior surface of the tire building drum on a tire constructed with the drum. Such imprints and bulges are undesirable in that they may later manifest as irregularities in a finished tire, which may, in certain circumstances, produce undesirable effects, such as for example vibration, noise, and/or resonance of the rolling tire.
In light of the above, an improved segment for a belt and tread drum, and a belt and tread drum which includes features for limiting deviation from the general cylindrical shape of the drum throughout expansion and contraction of the drum, thereby limiting the development of vibration, noise, and/or resonance of a tire manufactured using the belt and tread drum, are desired.